The rate is based in part on a small survey of about 5,500 households in California and is frequently revised. In November, the government initially reported a 0.4 percentage point drop in the rate but later changed it to a 0.2 percentage point decrease, Callori says.

The U.S. Bureau of Labor Statistics called the decline statistically significant. The only state with a bigger drop (0.5 percentage point) was South Carolina, although three states in addition to California had a 0.4 percentage point decline.

Despite the plunge, California's September rate was still third highest in the nation, behind Nevada at 11.8 percent and Rhode Island at 10.5 percent. These three are the only states that still have double-digit unemployment rates.

A broader survey of about 42,000 employers in California painted a less rosy picture.

It showed that California's private sector created about 14,900 new jobs in September, but the public sector lost about 6,400 - for a net gain of 8,500 nonfarm jobs since August.

This followed a revised gain of 5,100 jobs the previous month, but 8,500 "is a very small job gain" on a base of roughly 14.3 million nonfarm jobs, says Michael Reich, a labor economist at UC Berkeley.

Year over year, the survey showed an increase of 262,000 jobs, or 1.9 percent.

Categories understated

The drop in the unemployment rate "is welcome and part of the trend we've seen in California over the past two years. But it doesn't reflect the true dynamics" of the labor force, says Michael Bernick, a lawyer and former Employment Development Department director.

Like the national unemployment rate - which fell to 7.8 percent in September from 8.1 percent in August - the state rate understates unemployment and underemployment, he says.

Bernick notes that the national labor force participation rate - the percentage of adults working or actively seeking work - was only 63.6 percent in September, up barely from 63.5 percent in August. Historically, this rate is at least 66 percent.

The low participation rate reflects the fact that many unemployed people have stopped looking for work, retired early or gone back to school. When jobless people drop out of the labor force, the unemployment rate falls (all else being equal).

Bernick also notes that the number of Americans working part time, even though they seek full-time work, jumped by 581,000 from August to September. In the unemployment rate, they are counted as employed.

The drop in September's national unemployment rate raised some eyebrows. Former General Electric Chief Executive Officer Jack Welch, in tweets and a Wall Street Journal article, questioned whether the administration was trying to make the numbers look better ahead of the election.

Numbers fluctuate

Reich says the numbers "are bulletproof in terms of security," but "it's not unusual for the numbers in the household survey to fluctuate a lot from month to month."

Within California, unemployment rates in September ranged from 5.8 percent in Marin County to 28.5 percent in Imperial County.